// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2016 Thomas Gleixner.
 * Copyright (C) 2016-2017 Christoph Hellwig.
 */
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/sort.h>
#include <linux/group_cpus.h>

#ifdef CONFIG_SMP

static void grp_spread_init_one(struct cpumask *irqmsk, struct cpumask *nmsk,
                                unsigned int cpus_per_grp)
{
        const struct cpumask *siblmsk;
        int cpu, sibl;

        for ( ; cpus_per_grp > 0; ) {
                cpu = cpumask_first(nmsk);

                /* Should not happen, but I'm too lazy to think about it */
                if (cpu >= nr_cpu_ids)
                        return;

                cpumask_clear_cpu(cpu, nmsk);
                cpumask_set_cpu(cpu, irqmsk);
                cpus_per_grp--;

                /* If the cpu has siblings, use them first */
                siblmsk = topology_sibling_cpumask(cpu);
                for (sibl = -1; cpus_per_grp > 0; ) {
                        sibl = cpumask_next(sibl, siblmsk);
                        if (sibl >= nr_cpu_ids)
                                break;
                        if (!cpumask_test_and_clear_cpu(sibl, nmsk))
                                continue;
                        cpumask_set_cpu(sibl, irqmsk);
                        cpus_per_grp--;
                }
        }
}

static cpumask_var_t *alloc_node_to_cpumask(void)
{
        cpumask_var_t *masks;
        int node;

        masks = kzalloc_objs(cpumask_var_t, nr_node_ids);
        if (!masks)
                return NULL;

        for (node = 0; node < nr_node_ids; node++) {
                if (!zalloc_cpumask_var(&masks[node], GFP_KERNEL))
                        goto out_unwind;
        }

        return masks;

out_unwind:
        while (--node >= 0)
                free_cpumask_var(masks[node]);
        kfree(masks);
        return NULL;
}

static void free_node_to_cpumask(cpumask_var_t *masks)
{
        int node;

        for (node = 0; node < nr_node_ids; node++)
                free_cpumask_var(masks[node]);
        kfree(masks);
}

static void build_node_to_cpumask(cpumask_var_t *masks)
{
        int cpu;

        for_each_possible_cpu(cpu)
                cpumask_set_cpu(cpu, masks[cpu_to_node(cpu)]);
}

static int get_nodes_in_cpumask(cpumask_var_t *node_to_cpumask,
                                const struct cpumask *mask, nodemask_t *nodemsk)
{
        int n, nodes = 0;

        /* Calculate the number of nodes in the supplied affinity mask */
        for_each_node(n) {
                if (cpumask_intersects(mask, node_to_cpumask[n])) {
                        node_set(n, *nodemsk);
                        nodes++;
                }
        }
        return nodes;
}

struct node_groups {
        unsigned id;

        union {
                unsigned ngroups;
                unsigned ncpus;
        };
};

static int ncpus_cmp_func(const void *l, const void *r)
{
        const struct node_groups *ln = l;
        const struct node_groups *rn = r;

        return ln->ncpus - rn->ncpus;
}

static void alloc_groups_to_nodes(unsigned int numgrps,
                                  unsigned int numcpus,
                                  struct node_groups *node_groups,
                                  unsigned int num_nodes)
{
        unsigned int n, remaining_ncpus = numcpus;
        unsigned int  ngroups, ncpus;

        sort(node_groups, num_nodes, sizeof(node_groups[0]),
             ncpus_cmp_func, NULL);

        /*
         * Allocate groups for each node according to the ratio of this
         * node's nr_cpus to remaining un-assigned ncpus. 'numgrps' is
         * bigger than number of active numa nodes. Always start the
         * allocation from the node with minimized nr_cpus.
         *
         * This way guarantees that each active node gets allocated at
         * least one group, and the theory is simple: over-allocation
         * is only done when this node is assigned by one group, so
         * other nodes will be allocated >= 1 groups, since 'numgrps' is
         * bigger than number of numa nodes.
         *
         * One perfect invariant is that number of allocated groups for
         * each node is <= CPU count of this node:
         *
         * 1) suppose there are two nodes: A and B
         *      ncpu(X) is CPU count of node X
         *      grps(X) is the group count allocated to node X via this
         *      algorithm
         *
         *      ncpu(A) <= ncpu(B)
         *      ncpu(A) + ncpu(B) = N
         *      grps(A) + grps(B) = G
         *
         *      grps(A) = max(1, round_down(G * ncpu(A) / N))
         *      grps(B) = G - grps(A)
         *
         *      both N and G are integer, and 2 <= G <= N, suppose
         *      G = N - delta, and 0 <= delta <= N - 2
         *
         * 2) obviously grps(A) <= ncpu(A) because:
         *
         *      if grps(A) is 1, then grps(A) <= ncpu(A) given
         *      ncpu(A) >= 1
         *
         *      otherwise,
         *              grps(A) <= G * ncpu(A) / N <= ncpu(A), given G <= N
         *
         * 3) prove how grps(B) <= ncpu(B):
         *
         *      if round_down(G * ncpu(A) / N) == 0, vecs(B) won't be
         *      over-allocated, so grps(B) <= ncpu(B),
         *
         *      otherwise:
         *
         *      grps(A) =
         *              round_down(G * ncpu(A) / N) =
         *              round_down((N - delta) * ncpu(A) / N) =
         *              round_down((N * ncpu(A) - delta * ncpu(A)) / N)  >=
         *              round_down((N * ncpu(A) - delta * N) / N)        =
         *              cpu(A) - delta
         *
         *      then:
         *
         *      grps(A) - G >= ncpu(A) - delta - G
         *      =>
         *      G - grps(A) <= G + delta - ncpu(A)
         *      =>
         *      grps(B) <= N - ncpu(A)
         *      =>
         *      grps(B) <= cpu(B)
         *
         * For nodes >= 3, it can be thought as one node and another big
         * node given that is exactly what this algorithm is implemented,
         * and we always re-calculate 'remaining_ncpus' & 'numgrps', and
         * finally for each node X: grps(X) <= ncpu(X).
         *
         */

        for (n = 0; n < num_nodes; n++) {
                if (node_groups[n].ncpus == UINT_MAX)
                        continue;

                WARN_ON_ONCE(numgrps == 0);

                ncpus = node_groups[n].ncpus;
                ngroups = max_t(unsigned, 1,
                                 numgrps * ncpus / remaining_ncpus);
                WARN_ON_ONCE(ngroups > ncpus);

                node_groups[n].ngroups = ngroups;

                remaining_ncpus -= ncpus;
                numgrps -= ngroups;
        }
}

/*
 * Allocate group number for each node, so that for each node:
 *
 * 1) the allocated number is >= 1
 *
 * 2) the allocated number is <= active CPU number of this node
 *
 * The actual allocated total groups may be less than @numgrps when
 * active total CPU number is less than @numgrps.
 *
 * Active CPUs means the CPUs in '@cpu_mask AND @node_to_cpumask[]'
 * for each node.
 */
static void alloc_nodes_groups(unsigned int numgrps,
                               cpumask_var_t *node_to_cpumask,
                               const struct cpumask *cpu_mask,
                               const nodemask_t nodemsk,
                               struct cpumask *nmsk,
                               struct node_groups *node_groups)
{
        unsigned int n, numcpus = 0;

        for (n = 0; n < nr_node_ids; n++) {
                node_groups[n].id = n;
                node_groups[n].ncpus = UINT_MAX;
        }

        for_each_node_mask(n, nodemsk) {
                unsigned int ncpus;

                cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
                ncpus = cpumask_weight(nmsk);

                if (!ncpus)
                        continue;
                numcpus += ncpus;
                node_groups[n].ncpus = ncpus;
        }

        numgrps = min_t(unsigned int, numcpus, numgrps);
        alloc_groups_to_nodes(numgrps, numcpus, node_groups, nr_node_ids);
}

static void assign_cpus_to_groups(unsigned int ncpus,
                                  struct cpumask *nmsk,
                                  struct node_groups *nv,
                                  struct cpumask *masks,
                                  unsigned int *curgrp,
                                  unsigned int last_grp)
{
        unsigned int v, cpus_per_grp, extra_grps;
        /* Account for rounding errors */
        extra_grps = ncpus - nv->ngroups * (ncpus / nv->ngroups);

        /* Spread allocated groups on CPUs of the current node */
        for (v = 0; v < nv->ngroups; v++, *curgrp += 1) {
                cpus_per_grp = ncpus / nv->ngroups;

                /* Account for extra groups to compensate rounding errors */
                if (extra_grps) {
                        cpus_per_grp++;
                        --extra_grps;
                }

                /*
                 * wrapping has to be considered given 'startgrp'
                 * may start anywhere
                 */
                if (*curgrp >= last_grp)
                        *curgrp = 0;
                grp_spread_init_one(&masks[*curgrp], nmsk, cpus_per_grp);
        }
}

static int alloc_cluster_groups(unsigned int ncpus,
                                unsigned int ngroups,
                                struct cpumask *node_cpumask,
                                cpumask_var_t msk,
                                const struct cpumask ***clusters_ptr,
                                struct node_groups **cluster_groups_ptr)
{
        unsigned int ncluster = 0;
        unsigned int cpu, nc, n;
        const struct cpumask *cluster_mask;
        const struct cpumask **clusters;
        struct node_groups *cluster_groups;

        cpumask_copy(msk, node_cpumask);

        /* Probe how many clusters in this node. */
        while (1) {
                cpu = cpumask_first(msk);
                if (cpu >= nr_cpu_ids)
                        break;

                cluster_mask = topology_cluster_cpumask(cpu);
                if (!cpumask_weight(cluster_mask))
                        goto no_cluster;
                /* Clean out CPUs on the same cluster. */
                cpumask_andnot(msk, msk, cluster_mask);
                ncluster++;
        }

        /* If ngroups < ncluster, cross cluster is inevitable, skip. */
        if (ncluster == 0 || ncluster > ngroups)
                goto no_cluster;

        /* Allocate memory based on cluster number. */
        clusters = kzalloc_objs(*clusters, ncluster);
        if (!clusters)
                goto no_cluster;
        cluster_groups = kzalloc_objs(struct node_groups, ncluster);
        if (!cluster_groups)
                goto fail_cluster_groups;

        /* Filling cluster info for later process. */
        cpumask_copy(msk, node_cpumask);
        for (n = 0; n < ncluster; n++) {
                cpu = cpumask_first(msk);
                cluster_mask = topology_cluster_cpumask(cpu);
                nc = cpumask_weight_and(cluster_mask, node_cpumask);
                clusters[n] = cluster_mask;
                cluster_groups[n].id = n;
                cluster_groups[n].ncpus = nc;
                cpumask_andnot(msk, msk, cluster_mask);
        }

        alloc_groups_to_nodes(ngroups, ncpus, cluster_groups, ncluster);

        *clusters_ptr = clusters;
        *cluster_groups_ptr = cluster_groups;
        return ncluster;

 fail_cluster_groups:
        kfree(clusters);
 no_cluster:
        return 0;
}

/*
 * Try group CPUs evenly for cluster locality within a NUMA node.
 *
 * Return: true if success, false otherwise.
 */
static bool __try_group_cluster_cpus(unsigned int ncpus,
                                     unsigned int ngroups,
                                     struct cpumask *node_cpumask,
                                     struct cpumask *masks,
                                     unsigned int *curgrp,
                                     unsigned int last_grp)
{
        struct node_groups *cluster_groups;
        const struct cpumask **clusters;
        unsigned int ncluster;
        bool ret = false;
        cpumask_var_t nmsk;
        unsigned int i, nc;

        if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
                goto fail_nmsk_alloc;

        ncluster = alloc_cluster_groups(ncpus, ngroups, node_cpumask, nmsk,
                                        &clusters, &cluster_groups);

        if (ncluster == 0)
                goto fail_no_clusters;

        for (i = 0; i < ncluster; i++) {
                struct node_groups *nv = &cluster_groups[i];

                /* Get the cpus on this cluster. */
                cpumask_and(nmsk, node_cpumask, clusters[nv->id]);
                nc = cpumask_weight(nmsk);
                if (!nc)
                        continue;
                WARN_ON_ONCE(nv->ngroups > nc);

                assign_cpus_to_groups(nc, nmsk, nv, masks, curgrp, last_grp);
        }

        ret = true;
        kfree(cluster_groups);
        kfree(clusters);
 fail_no_clusters:
        free_cpumask_var(nmsk);
 fail_nmsk_alloc:
        return ret;
}

static int __group_cpus_evenly(unsigned int startgrp, unsigned int numgrps,
                               cpumask_var_t *node_to_cpumask,
                               const struct cpumask *cpu_mask,
                               struct cpumask *nmsk, struct cpumask *masks)
{
        unsigned int i, n, nodes, done = 0;
        unsigned int last_grp = numgrps;
        unsigned int curgrp = startgrp;
        nodemask_t nodemsk = NODE_MASK_NONE;
        struct node_groups *node_groups;

        if (cpumask_empty(cpu_mask))
                return 0;

        nodes = get_nodes_in_cpumask(node_to_cpumask, cpu_mask, &nodemsk);

        /*
         * If the number of nodes in the mask is greater than or equal the
         * number of groups we just spread the groups across the nodes.
         */
        if (numgrps <= nodes) {
                for_each_node_mask(n, nodemsk) {
                        /* Ensure that only CPUs which are in both masks are set */
                        cpumask_and(nmsk, cpu_mask, node_to_cpumask[n]);
                        cpumask_or(&masks[curgrp], &masks[curgrp], nmsk);
                        if (++curgrp == last_grp)
                                curgrp = 0;
                }
                return numgrps;
        }

        node_groups = kzalloc_objs(struct node_groups, nr_node_ids);
        if (!node_groups)
                return -ENOMEM;

        /* allocate group number for each node */
        alloc_nodes_groups(numgrps, node_to_cpumask, cpu_mask,
                           nodemsk, nmsk, node_groups);
        for (i = 0; i < nr_node_ids; i++) {
                unsigned int ncpus;
                struct node_groups *nv = &node_groups[i];

                if (nv->ngroups == UINT_MAX)
                        continue;

                /* Get the cpus on this node which are in the mask */
                cpumask_and(nmsk, cpu_mask, node_to_cpumask[nv->id]);
                ncpus = cpumask_weight(nmsk);
                if (!ncpus)
                        continue;

                WARN_ON_ONCE(nv->ngroups > ncpus);

                if (__try_group_cluster_cpus(ncpus, nv->ngroups, nmsk,
                                             masks, &curgrp, last_grp)) {
                        done += nv->ngroups;
                        continue;
                }

                assign_cpus_to_groups(ncpus, nmsk, nv, masks, &curgrp,
                                      last_grp);
                done += nv->ngroups;
        }
        kfree(node_groups);
        return done;
}

/**
 * group_cpus_evenly - Group all CPUs evenly per NUMA/CPU locality
 * @numgrps: number of groups
 * @nummasks: number of initialized cpumasks
 *
 * Return: cpumask array if successful, NULL otherwise. And each element
 * includes CPUs assigned to this group. nummasks contains the number
 * of initialized masks which can be less than numgrps.
 *
 * Try to put close CPUs from viewpoint of CPU and NUMA locality into
 * same group, and run two-stage grouping:
 *      1) allocate present CPUs on these groups evenly first
 *      2) allocate other possible CPUs on these groups evenly
 *
 * We guarantee in the resulted grouping that all CPUs are covered, and
 * no same CPU is assigned to multiple groups
 */
struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
{
        unsigned int curgrp = 0, nr_present = 0, nr_others = 0;
        cpumask_var_t *node_to_cpumask;
        cpumask_var_t nmsk, npresmsk;
        int ret = -ENOMEM;
        struct cpumask *masks = NULL;

        if (numgrps == 0)
                return NULL;

        if (!zalloc_cpumask_var(&nmsk, GFP_KERNEL))
                return NULL;

        if (!zalloc_cpumask_var(&npresmsk, GFP_KERNEL))
                goto fail_nmsk;

        node_to_cpumask = alloc_node_to_cpumask();
        if (!node_to_cpumask)
                goto fail_npresmsk;

        masks = kzalloc_objs(*masks, numgrps);
        if (!masks)
                goto fail_node_to_cpumask;

        build_node_to_cpumask(node_to_cpumask);

        /*
         * Make a local cache of 'cpu_present_mask', so the two stages
         * spread can observe consistent 'cpu_present_mask' without holding
         * cpu hotplug lock, then we can reduce deadlock risk with cpu
         * hotplug code.
         *
         * Here CPU hotplug may happen when reading `cpu_present_mask`, and
         * we can live with the case because it only affects that hotplug
         * CPU is handled in the 1st or 2nd stage, and either way is correct
         * from API user viewpoint since 2-stage spread is sort of
         * optimization.
         */
        cpumask_copy(npresmsk, data_race(cpu_present_mask));

        /* grouping present CPUs first */
        ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
                                  npresmsk, nmsk, masks);
        if (ret < 0)
                goto fail_node_to_cpumask;
        nr_present = ret;

        /*
         * Allocate non present CPUs starting from the next group to be
         * handled. If the grouping of present CPUs already exhausted the
         * group space, assign the non present CPUs to the already
         * allocated out groups.
         */
        if (nr_present >= numgrps)
                curgrp = 0;
        else
                curgrp = nr_present;
        cpumask_andnot(npresmsk, cpu_possible_mask, npresmsk);
        ret = __group_cpus_evenly(curgrp, numgrps, node_to_cpumask,
                                  npresmsk, nmsk, masks);
        if (ret >= 0)
                nr_others = ret;

 fail_node_to_cpumask:
        free_node_to_cpumask(node_to_cpumask);

 fail_npresmsk:
        free_cpumask_var(npresmsk);

 fail_nmsk:
        free_cpumask_var(nmsk);
        if (ret < 0) {
                kfree(masks);
                return NULL;
        }
        *nummasks = min(nr_present + nr_others, numgrps);
        return masks;
}
#else /* CONFIG_SMP */
struct cpumask *group_cpus_evenly(unsigned int numgrps, unsigned int *nummasks)
{
        struct cpumask *masks;

        if (numgrps == 0)
                return NULL;

        masks = kzalloc_objs(*masks, numgrps);
        if (!masks)
                return NULL;

        /* assign all CPUs(cpu 0) to the 1st group only */
        cpumask_copy(&masks[0], cpu_possible_mask);
        *nummasks = 1;
        return masks;
}
#endif /* CONFIG_SMP */
EXPORT_SYMBOL_GPL(group_cpus_evenly);